Arrange the following complexes in increasing order of their magnetic moment
(A) $[NiCl_4]^{2-}$
(B) $[Fe(H_2O)_6]^{2+}$
(C) $[Cr(H_2O)_6]^{3+}$
(D) $[Co(C_2O_4)_3]{3-}$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (D), (A), (C), (B)
Calculation of spin-only magnetic moment ($μ = \sqrt{[n(n+2)]} BM$):
|
Complex |
Metal ion |
d-electron count |
Geometry & pairing |
Unpaired e⁻ (n) |
μ (BM) |
|
(D) [Co(C₂O₄)₃]³⁻ |
Co³⁺ |
d⁶ |
Strong field (oxalate), low spin |
0 |
0 |
|
(A) [NiCl₄]²⁻ |
Ni²⁺ |
d⁸ |
Tetrahedral (Cl⁻ weak field) |
2 |
2.83 |
|
(C) [Cr(H₂O)₆]³⁺ |
Cr³⁺ |
d³⁸ |
Octahedral, high spin |
3 |
3.87 |
|
(B) [Fe(H₂O)₆]²⁺ |
Fe²⁺ |
d⁶ |
Octahedral, weak field (H₂O), high spin |
4 |
4.90 |
Increasing order of magnetic moment:
0 < 2.83 < 3.87 < 4.90
∴ (D) < (A) < (C) < (B)